They gloss over the problem of generating proton-antiproton pairs efficiently when the vacuum breaks down into electron-positron pairs at 1/1836th the energy of proton-antiproton pairs. Which I think would tend to 'drain' the available laser energy before you reach the required energy for proton-antiproton creation.

I'd think it also more likely that the weight of the fuel is less than the weight of the equipment to generate antimatter. Thinking really long-term, it would make sense to set up refueling stations around nearby stars to produce antimatter, but it seems silly to carry it all with you just to bring it back to Earth (where we presumably have one already).

Perhaps a misson can be proceeded by a chain of unmanned fueling stations launched in the months prior to the main misson. These stations would deploy solar arrays to harvest the sun's energy to create fuel for the main ship. One problem would be to figure out how to rendezvous without the main ship needing to decelerate.

One problem would be to figure out how to rendezvous without the main ship needing to decelerate.

The main ship does not necessarily need to rendezvous with the entire harvester. As long as the fuel can be stored and transported, the harvester can have specialized delivery equipment which can match the ship's speed. Then it's just a matter of ensuring that the ship and the container are in the same area at the same time.

The harvester could even have equipment to accelerate the container to near the required speed, so as to ensure maximum possible delivery. To make it reusable, the ship would need to leave the container with enough fuel for the return journey, which should be feasible since the container would be almost empty on the way back.

i'm sorry if the question sounds stupid, but that high level science is not my strong suit. do you mean that because electron-positron pair require less energy to form they would be created much more often that the needed proton - antiproton pairs from such process. And because smaller parts of the energy would constantly be used for the creation of the low energy pairs there would almost always be unsufficient energy for the high yield energy pair. Wouldnt that problem simply be solved by making the laser output more powerful than the need for the proton pairs thus always having enough energy for their creation even if you non stop create electron-positron pairs?

[...]namely the interstellar rendezvous and return mission that could be accomplished on timescales comparable with a working
scientist’s career. Such a mission would involve an initial boost phase followed by a coasting phase to the target system. Next
would be the deceleration and rendezvous phase, which would be followed by a period of scientific data gathering. Finally,
there would be a second boost phase, aimed at returning the spacecraft back to the solar system, and subsequent coasting and
deceleration phases upon return to our solar system.

I find sentences like this more than a little obnoxious.. In order to go there and go back, we first need to go there and stop there, then we can be there for a while, then we start going back, then we're on the way back again, and we can stop going back again until we're home.

Such a mission would represent a precursor to a future manned interstellar mission; which in principle could safely return any astronauts back to Earth.

Yes, but that is not what you're describing here, stop wasting abstract-space. Delete say-nothing bits of text please..

Edit: Uhm... they seem to be wrong;(edit: i am wrong, they mean to 'fuel up' close to the sun, and away from it there is less sunlight) they seem to be talking about making particles from energy basically 'freely available' on the ship and using them for propulsion. Whereas in classical mechanics the center of mass(CM) is conserved in the rest frame, in relativistic mechanics the center of energy is. It is better to get the energy away faster, the fastest way is with the speed of light. Stated differently, lower rest mass of thrust particles means less energy for more momentum.

Now, at 1.88 GeV for an electron(or even pions) it might be(edit:is) pretty close to the speed of light, but what i said above would mean using the mirrors as... mirrors and just reflecting back in an appropriate direction would be just as effective..(ftr, for us the energy in the mass is inaccessible, which is why for us light beams are incredibly inefficient, we just don't count the rest mass energy)

From a biological standpoint of humanity as a species of mammal, wouldn't interstellar travel and colonization be the single most important long term goal our species should be focusing on?

Obviously, someday our star will die, but before that there are a certainly countless large objects drifting through space that could annihilate our species, and the sooner we start branching off into other areas of space, the safer we are, right?

Sometimes a problem is just not ready to be approached. For instance, suppose that in Euclid's time, the Greeks figured out that someday, about 2300 years in the future, it would be very important to be able to carry out arithmetic calculations at a sustained rate of 1 billion operations per second with low latency.

What could Euclid and his fellow Greeks do to help that come about?

Nothing specifically. The problem is so far beyond the technology and science available to them that they would not be able to purposefully make any contribution toward a solution at all. Anything approach they would come up with would be wrong and just lead to a dead end, and probably actually delay the eventual solution.

Their best approach would be to just ignore it and concentrate on improving their science and technology in general, and make sure that each new generation is aware that the problem needs to be solved by the 21st century.

What do people think we mean? Lock a bunch of the brightest in the world in a room and hope they come up with an answer by lunchtime?

The road to interstellar travel is long, when we say we should be working towards that, we mean that as a long-term goal. We should ready ourselves not just technologically, but politically and socially. We need a major overhaul of society in general before we are ready to colonize other planets.

When someone says, "we should work towards colonizing other planets," they generally don't mean on a time-scale of days or weeks.

I know, but even on the scale of years there is a massive pay off for us, if the cold war space race hadn't ended so soon us 20 year old kids might be talking about how amazing our moon bases are instead of how we never even got to see a moon landing.

The only way that can come about is if we find a source of nearly free, unlimited energy. The current costs of sending objects in to space is beyond our reach for the most part. $1000 a pound means it costs almost a quarter of a million dollars to send a single person in to space. Most of that cost is the propellant.

Maybe some sort of massive rocket fuel manufacturer built near a volcano or yellowstone. Geothermal powered hydrogen production.

Agreed.
The weakest link in the chain necessary for human space exploration is, of course, humans and the demands of our physiology. That's why building massively expensive and complex technologies to accommodate our poorly adapted (to non-Earth environments) bodies seems wrong-headed to me. Far better to focus on genetics and biological sciences, e.g., so that we can just modify ourselves, rather than our whole environment.

When we do reach far into space, the "we" will have to be very different from what it is now.

No, we won't get to the next star in our lifetimes. But we'll never get there if we just sit around on Earth lobbing unmanned probes at other planets and whinging that "it's too hard."

In 1961, when the farthest man had gone in space was one orbit, and the US hadn't sent anyone into space, JFK looked at the Moon and said "see that airless rock 250,000 miles away? Let's go there. In ten years."

If NASA had spent eight years saying "it's too hard" and lobbing probes into orbit, then in 1969 we would've been able to ... lob another probe into orbit.

We have to make baby steps if we're ever going to make the big steps. We have to put people on Mars. We have to put colonies on the Moon and Mars. We have to send people to the moons of Jupiter and Saturn. If we don't make these baby steps, we will never make it past Neptune.

Their best approach would be to just ignore it and concentrate on improving their science and technology in general

Or in this case, figure out how to get to damned LEO first. The stars can come later. It drove me crazy every time I saw NASA waxing poetical about advanced spaceship drives or going to Mars. For 3 decades they could barely manage to make it 100 miles up, much less 100 million, and now they can't even do that anymore.

Sometimes a problem is just not ready to be approached. For instance, suppose that in Euclid's time, the Greeks figured out that someday, about 2300 years in the future, it would be very important to be able to carry out arithmetic calculations at a sustained rate of 1 billion operations per second with low latency.

Not a great example, we can comprehend the idea that other stars exist, have planets around them that we may like to visit, we've even directly imaged a few. You also say "suppose," the problem there is that they didn't, so we don't know what would have happened.

If I were those Greeks, the first step would be to automate the processes that can be automated and expand from there. Greeks had primitive examples of machines, the Antikythera device being a fantastic example. I suppose they would have used a similar device as a jumping off point.

Please give the ancient folk some credit, they were as smart as you or I. The problem is you require necessity and a comprehension of certain ideas. That is something that we have and they would not have had.

Very true. In fact it's entirely possible the Antikythera device was based on a design by Archimedes, if not designed by the man himself, in which case "as smart as you or I" may be an understatement.

In fact, given the incentive I'd be willing to bet Archimedes could have come up with a rough design for a mechanical computer, along the lines of Babbage's difference engine. Imagine how different things could have turned out if the ancient Greeks had built the first computers.

Ofcourse that would be great. But we should focus on a smaller timeframe. The sun isn't gonna explode for another 4.5 billion years (ish) whereas we will probably change our habitat (earth) in a way that may very well prohibit human life before then.

And having a workable interstellar drive would no doubt help to improve any existing interplanetary drives we might have, there for helping to make colonization of the solar system more efficient and practical.

Ok so we have 1 billion years as opposed to 3/4. Ok, I think we can work with that. If we accept 0 CE as the base point, in 2000 years we've gone from building giant pyramids to landing on the moon. Hopefully in another hundred years we'll figure out a renewable energy source, that leaves us...pretty much a billion years to get the interstellar part down.

The underlying problem is not technology, but our society as a whole. Profit is our only motivation, and has been for at least 6000 years. Why do you think the internet is being a hot topic today? Because it's basically unlimited (not unlimited, but close enough) on the ones and zeroes, and without a limit to resources, there's no profits to be made, as profits are made from demand measured on limits.

While an effective renewable energy source is cool, it would cause a ripple on society. Suddenly, everyone would be able to afford to survive, and the energy business would die. Long term, however, it would rapidly exhaust our planet of mineral resources as the economy changes focus to the consumption of our (near) unlimited energy.

My point is, as a species we have already doomed ourselves, unless our singular focus on profit (which has lasted for thousands of years) is not radically changed, as there's just no way to maintain our current structure.

credibility: I work with energy production, and r/science taught me how to build a tin foil hat ;)

As long as there's energy for us to convert materials yeah. But we should avoid throwing too much "garbage", ie. spaceships, engine exhaust, etc... into space, otherwise we'll slowly drain some resources, although that might not even matter that much.

Given the size of the earth and the availability of materials in asteroids... and Mars... and the rest of the rocky planets in our solar system, I don't think it will be a problem for the conceivable future?

I was speaking of now, not in a ~200 years period of time, if we discovered a means to endless energy tomorrow, effecient recycling would depend on the pace of adaption for profit, which today are far behind our consumptions, despite our advancements in understanding. Society is to blame, as long as you make greater profits by reducing the resources worldwide, why spend money on recycling if the process is too expensive and reduces our overall profit from shortage?

For example, the facility I work on is the only one of it's kind. It was a risky move, that basically started out as a publicity stunt. It is highly unlikely that another facility like ours will rise from the ashes elsewhere in the world anytime soon. We do make good profits recycling a certain biproduct however, and as we experiment further, one day it might become common place; but for now, tons of the biproduct we use in our facility goes to waste all over the planet every year.

Unlimited energy is also quite quite distant, so it isn't unreasonable for me to be making projections about advancements in recycling as well (which will become necessary as the earth runs low certain rare minerals).

In the meantime, that capitalism is in danger from a lot more than just unlimited energy. Robotics much? We're already beginning to feel the pangs of computers greatly increasing the amount of work people can do. Soon enough, automation software will catch up with the physical hardware. We can see it in the Google driverless car. The day that hits the road, that's millions of taxi-drivers, limousine drivers, trucks drivers, mailmen, pizza delivery men out of work, all over the world.

What do we do as fewer and fewer need to work to keep our society functioning? How can capitalism function? Unlimited energy is just one problem that faces our profit driven society. In the century to come, we're going to see many many more.

IMO, while that may be theoretically true, space or interplanetary colonization would almost certainly not happen for that reason. It might happen if it were profitable or an affordable scientific priority. It might be an emergency measure because of some natural or human disaster. It might even be a privately funded reality television show. But it won't happen because it's probabilistically better for the survival of the species as a whole. Not unless the insurance industry seizes the reins of power in a world-wide coup.

In seriousness, there are many obstacles that need to be addressed. It seems to me that we don't have many good reasons right now to believe that human beings can survive and reproduce in a space structure or on another planet permanently. Also, surviving in space and surviving on another planet are entirely different issues, and yet you would have to be able to do the one in order to do the other. And then, every planetary environment would be different. The capacity for emergency evacuation from a space colony would be almost zero.

Space colonization is one of the holy grails of technology. If it is something that we can achieve, it would provide a definitive answer to all of those "man versus nature" themes in Shakespearean plays and sonnets that we wrote about in 10th grade English class.

Dismiss it all you want, but my point is that there has been real advancement in aeronautics technology since the moon landing.

One can validly argue that there could have been more and that there's been the wrong balance between manned and unmanned efforts. But that doesn't negate the impressive technologies that brought us the ISS, Spirit, Opportunity, Hubble, Curiosity and more.

If you allow me to count non-manned machinery, there's actually several different examples of space-faring tech that's doing pretty damn well for itself (satellites and missiles being the two most prominent examples). We just need proper motivation for the government to actually put money behind this project. Look at the crazy-ass shit the military's pumping out now with its absurd budget; think about what other sectors would do with similar ones.

Yeah for sure but I can't help thinking sometimes that the challenge of interstellar travel is so achingly massive that it may require a very prolonged period of developement before any tangible success is reached. I hope it's not too long though!

It's a big achievement, but we have gotten extremely far with studies in material science and science in general. I'm also interested in a space elevator so we don't have to burn a lot of fuel to get into space.

You think? I'm pretty sure a lot of people wouldn't be content with that and would want to go exploring, and interstellar travel becomes much easier if you only have to transport a computer the size of a soda can and you can just pause your crew until they get there.

Depends on how you define we. 3 billion years is a lot of time to evolve. "We" could be many species or none, "We" could be the persistence of a consciousness alive today artificially kept functional for that long, "We" could be the artificial intelligence that arises from precisely modelling the human brain. I doubt what we will be in 3 billion years would be considered human now, but that's not the whole picture.

True. However, one can extrapolate from the current state of human affairs and argue that we will destroy ourselves by then. But I will concede that it's impossible to know for certain what will happen in 3 gigayears.

You can't really extrapolate that far into the future based on the miniscule slice of time you've been privy to in your life and via history textbooks etc. This is small picture and dare I say cynical thinking. A lot can happen in even 100 years.

You can't be sure but I'd tend to think this. It seems the more power we humans get, the more we can kill with more ease. If one person or one entity has too much power, this raises the chance when that the species could be fucked if they're careless or malicious with the power. The phrase, "The Great Filter", comes to mind which I picked up from reading an article years ago. That the universe may have some filter in place to keep on organism from maintaining too much intelligence and power. The insatiable appetite for power and control, to learn of our environment to overcome it and others, has made us very malicious in the past and present.

Sometimes I think it's like the Presidency. I think the ones smart enough to know how much power they have and how much control it needs are the ones leery of such a position and the more they know the more they realize they don't know. There seems to be a balance in the universe, a filter, and I don't know where it ends with intelligence. The ones who know the world is over-populated don't breed as much while the ignorant keep breeding. Intelligence is not necessarily a productive trait.

In light of SENS and genemod, a " scientist's working career" is on the verge of being radically redefined.

Sit back, relax. The 21st century is going to be far more awesome than you realize. Many of you will see the 22nd. And the 23rd. Begin thinking in terms of centuries. You are just now in the larval phase.

only if you travel to a star that's significantly more light years away than a human lifespan. if you assume to be traveling at the speed of light to Proxima Centari, you would arrive instantaneously, while the rest of the earth would age 4 years or so. easily enough time to get back before your family died.

Yes, in fact you would, if you were traveling at the speed of light, which is impossible. You're always traveling through time and space, and the faster you move through one, the slower you move through the other. If you're moving through space at the fastest possible velocity, then you're not moving through time at all.

Reminds me of the ideas that the books after Ender's Universe always talked about the problems of colonies only seeing a new ship from earth every 100 years or so. That by the time the people who got on the ship, arrived at the new colony, everyone they knew was dead. Loved the Philosophy and ideas that book took in this.

Fun fact: relativity only applies if you double back. If you leave for a star, then 5 years later another group leaves for the same star, you will not experience any time shiftiness and they would reach you 5 years after you left.

Something I've always wondered about the Twin Paradox: if the universe were closed and finite, thus able to be circumnavigated, what would happen with regard to the TP? The travelling twin could head in a straight line, never turn around, and return to Earth. With no turning back to break the symmetry, what resolves the paradox?

They would arrive 5 years after you arrive, not 5 years after you left. If it took 20 years to get to a star then what you said would mean they would arrive before you arrived.

From peoples on earth point of view, they would leave 5 years after you. But in your point of view, they would leave a lot shorter than that depending how fast you are going and how long it took to accelerate to that speed.

Assuming warp is possible (einstein rosen bridge), then that's not the case. I hate to say it, but interstellar travel is pretty unpractical unless it's significantly faster than the speed of light, and the only way science allows this (as far as we know) is through the use of an einstein rosen bridge.

THere is also the issue radiation and galactic cosmic rays. Propulsion isn't the only problem, without proper shielding, the technology for which doesn't exists, there is no way to survive traveling through the interstellar medium.

"the technology for which doesn't exist", thats what I said. The most advanced shielding I know of that is currently being developed is the magnetic shielding to be used in fusion reactors, it holds less than a few seconds before failing. So I agree, if perfected this kind of shielding could be used, but would have to be massive to enclose the ship. If using a fusion reactor for power (bringing lots of deuterium with you), magnetic shielding for protecting the hull, occupants, and the fusion reactor, and an anti-matter engine of sorts, maybe we'll start to have something....it's gonna have to be a really really big spaceship.

Magnetic shielding will only stop charged particles, a reversed CERN particle accelerator would easily provide enough shielding, of course it would need to be much lighter and efficient for a space ship .

There is a technology for that, it is called "passive shielding". Just make the hull a few meters thick and that's it.

(One could object that the ship would be too massive with a hull that thick, but a manned interstellar ship most likely will have to be huge, and the hull mass would be kind of small compared with the total volume of the thing.)

P.S. Sending an antimatter factory to an occupied system is an act of war. The energy needed for interstellar travel is enough to make planet-buster bombs.

This is a pretty important point, in my opinion. Sure, space is pretty empty, so accidentally hitting a planet is unlikely, but still -- all it takes is one mistake, and you could wipe out a planet with your insanely high velocity. Kinda makes you wonder if attaining this level of technological sophistication leads to species quickly wiping themselves out, simply due to the massive consequences of a single big accident. I guess maybe at that point, maybe we'll have "diversified" our location and will be inhabiting other planets/moons/space stations/dyson spheres.

No, space really is that big. Hitting a planet will never be an issue. Imagine being a piece of dust flying over Kansas and there are like a few balloons that represent stars, with some bees flying around the balloons for whatever reason. You can go across the entire state without worrying about hitting those things.

The thing about energy losses is you have to radiate that heat. Keeping thrusters from melting is hard when you have a ton of energy going through them.

Everything I know about physics tells me working with anti-matter will be just short of impossible or impossible. Imagine designing a tank whose contents can't touch the walls of the container. If the immensely powerful magnetic fields fail, your spacecraft is immediately annihilated in the largest man-made explosion ever created. The same goes for the pipes from the generator and to the thruster. The power required to maintain the containment, keep people alive for years, and even the thrust based on anti-matter fuel.

My first thought too, but if you read the whole article it isn't about a perpetual motion machine. It's just an antimatter powered ship that happens to bring along a solar powered antimatter generator that can be deployed when you get to the destination star to refuel your tank. So you have solar energy->laser->antimatter->whatever wacky engine is supposed to burn antimatter and inevitably less than 100% conversion efficiency at each of those arrows. Definitely nothing like >100% energy out than what went in.

A boost phase, followed by a cruise phase. I can comprehend the cruise phase being the longest part of the journey, but Can anyone give me an idea of how fast a vehicle like this would presumably be traveling during the boost phase?

In order to maintain a cruise phase over a distance as long as I'm imagining, that boost phase must be ridiculously fast. Can humans sustain speeds that fast, even in space?

*edited for grammar

Sorry, not a scientist by a long shot. Just curious as to the present understanding of those two questions.

It's not speed itself that would be a problem, it's acceleration. 1g, the acceleration of gravity we're used to, is about 9.8 meters/sec2. I cannot find any references, but IIRC a ship would only have to accelerate at 1g for a couple years before reaching significant fractions of c at which point time dilation becomes noticeable (about 90% the speed of light).

Additionally, cruise speed remains constant, as space is a vacuum. After the accceleration phase, a ship can coast along at ~0.99c for as long as it needs to before beginning its deceleration phase, which should take as long as its acceleration phase. It has also been suggested that the acceleration phase and deceleration phase could take up the entire trip; this way, travelers would experience normal gravity for the duration of the flight. The downside to this is that it becomes increasingly difficult to accelerate at 1g as the ship approaches the speed of light.

What about the problem of time? While travelling at such speeds, the individuals would experience time on a much slower pace than those still on Earth. Who knows how many extra years would go by while they were travelling in space?!?

As much as I would LOVE for this to be a reality we need to approach this logically. We can't put a man on the moon because it costs to much money, how the HELL are we going to send people into interstellar space. The mission to Mars is thought to occur in 2030, and they are now preparing just the food for that mission. THE FOOD. Again, sending people into interstellar space soon? I don't think so. Let's get to the speed of light first.

It costs too much money to put a man on the moon using today's technology, but I think what this article is trying to show us is that with the recent event at CERN, the thought of interstellar travel is much more plausible.

We can't put a man on the moon because Congress doesn't want to order NASA to do it. NASA has more than enough money, but they can't act without congressional approval. Right now the only reason Congress allows NASA to exist is because it's jobs. They're slowly phasing it out though, and we may not have NASA by next decade.

We are going nowhere - not even Mars - until we solve the gravity problem. Our bodies have evolved over millions of years to live in a gravity field. We cannot exits long without one.

People returning from the space station cannot walk around until they get use to gravity again.

If we sent astronauts to Mars, they would have to land and wait several days before venturing out of the landing craft. They would be helpless for a few days. The guys who walked on the moon had only been weightless a short period. Either we have to come up with artificial gravity, or through reprogramming the human DNA molecule, produce a human being that can live for an extended period without gravity. Of course, they could never land or walk on the surface of any planet.

I remember reading that there was a theoretical barrier of 20 miles per hour on trains. If that barrier was broken the fear was that the vacuum created would suffocate people on board and might be sufficient to hurl bodies out of the train.

Laser-propulsion rockets... reminds me an episode from "2001 Nights". Amazing manga! This is where I've first heard about laser propulsion system.

This is one of the short-stories:

Basically it's story about mankind's space travel in future. A space explorers were observing a star going supernova. Suddenly, they see an alien vessel shooting past them using a laser propulsion. Excited with the prospect of discovering advanced aliens, they trace the originating planet, but they get caught in the star's flare and end up crash landing in the planet.

The planet doesn't have much time, as the sun would go supernova in a matter of days. The survivors see a gigantic blast of laser periodically shooting rockets up into the space in a far distance; it appears the aliens are evacuating the planet. The survivors decide to go to the launching place in hopes of contacting aliens and leaving the planet before it gets engulfed by the supernova.

During their trek, they discover that the entire planet is covered with huge vegetation with gigantic flowers. The plants are all connected and appears to be one gigantic organism gathering the tremendous amount of solar energy from the exploding sun. Many of the survivors die due to earthquakes and other accidents on their way to launching site high atop a mountain.

SPOILER:

So when the last two survivor reaches the launching site, they discover no animal form of life, but a huge plant structure generating bio-laser. Basically, the planet is covered with a network of plants joined as a single organism. It is gathering up the solar energy to power the bio-laser to launch its seed into space in hopes of delivering its seeds into a habitable planet.

2001 Nights have many more fascinating tales regarding humanity and space travels. I definitely recommend it!

We went from conceiving the equivalence of matter and energy, to designing serious propulsion systems based on antimatter creation from the vacuum in 100 years. Wicked. Certainly the approach has its challenges, but it looks like one of the most promising approaches I've read about.

This is just silly. Even if you had an engine and a fuel source capable of such travel, you wouldn't survive it. One speck of interstellar dust would pulverize a ship travelling at 0.10c let alone higher speeds.

Edit: If you want to educate yourself, please read up on the subject in The Starflight Handbook and stop downvoting me for giving you bad news.

We can calculate the density of interstellar dust from absorption of stellar light. It is fairly low, as should be obvious from the fact that we can see far away stars without too much of their light being absorbed. A good review of what we know about interstellar dust is here:

Placing a debris shield ahead of the starship can absorb dust impacts. From Figure 8 of the above paper, dust grains are primarily below 2 microns in size. Assuming a 2 micron grain were made of iron (which is an overestimate), an impact at 50% of the speed of light releases ~1500 joules of energy, equal to about 0.4 grams of TNT.

At those speeds, "particle" is the wrong way to think of an interstellar dust grain. It acts like a particle beam with the atomic nuclei having an energy of ~230 MeV per nucleon. The chemical bonds between the atoms in the grain are insignificant at that speed.

Whatever the dust grain hits first will shred it + what it hits into an ionized cloud which will disperse in exactly the same way a particle beam with that energy hitting a stationary target would.

Nice info, but insufficient. Firstly, a debris shield ahead of your starship only shields against the additive energy of your velocity to the grains... helpful, but not comprehensive. So you still have to deal with grains coming at you from all angles at high speeds. Furthermore, if you're planning the flip your ship around to decellerate, your front shield is going to have to move around... and now deal with the fact your exhaust is hitting it from behind. Even if you carry a shield all around you and leave a small window for exahust, you still leave yourself vulnerable to that small window of entry.

Then you have to deal with the constant degradation of the shield. A few grams of TNT may not seem like much, but now imagine it going off every second of your multi-year journey and your shield ain't gonna last very long.

Finally, of course, you run the risk of larger grains (0.1 kg) which are much worse. And that's the issue... are you going to risk the trip to Alpha Centauri with a 10% chance you'll run into a larger grain and die?

If you want to educate yourself, please read up on the subject in The Starflight Handbook and stop downvoting me for giving you bad news.

(1) I upvoted you, because that increases the chance my own comment would be seen.

(2) At 50% of lightspeed, nothing will be coming at you "from all angles". The ship velocity would be so vastly greater than random dust grain motion that all the flux would appear to be from the front.

(3) When you are slowing down, you are emitting a beam of high energy particles created by antimatter reactions*, assuming the propulsion system in the article. Presumably that can be made to clear your path. If not, mount the shield behind the deceleration thrusters.

(4) In my copy of the "Starflight Handbook" (hardcover, 1989) it says (p. 169) "In the worst case, a one centimeter thick shield is required for the half century flight of the Daedalus probe to Barnard's Star."

All you need to do is ionize dust in front of you then use a magnetic field to deflect those charged particles. It isn't going to stop something the size of an asteroid, but those pesky tiny dust particles sure are.